Power supply device

ABSTRACT

The power supply device of the present invention includes a main converter and at least one sub converter connected in parallel between a pair of output ends of a DC power supply circuit for receiving power through a parallel circuit of a thyristor and a thermistor having a positive temperature coefficient. Each of the main converter and the at least one sub converter includes: a series circuit composed of a diode and a switching element and connected between the pair of output ends; a series circuit composed of a capacitor and an inductor and connected in parallel with the diode; and a drive circuit configured to drive the switching element. The main converter controls the thyristor in accordance with a voltage across a secondary winding magnetically coupled with the inductor. When a short circuit of the switching element of the at least one sub converter occurs, the drive circuit of the main converter terminates driving of the switching element of the main converter.

TECHNICAL FIELD

The present invention relates to power supply devices.

BACKGROUND ART

In the past, there has been proposed a power supply device whichconverts power inputted from an external power supply and outputsconverted power and includes a thermistor having a positive temperatureproperty (so-called a PTC thermistor) in order to suppress rush currentat the time of activation interposed in a power supply path from such apower supply (e.g., see document 1 [JP 2008-104273 A]). In this regard,when excess current such as rush current flows, Joule heat causes a risein temperature of the thermistor, and this leads to increase in aresistance of the thermistor. Consequently, such current can besuppressed. The thermistor may have such a temperature property thatresistance greatly varies with temperature. For example, a resistance ofthe thermistor at 160° C. is approximate 100 times as high as aresistance of the thermistor at 25° C.

Further, a thyristor is connected in parallel with the aforementionedthermistor and a circuit of the power supply device is configured tokeep the thyristor on during stable operation. Rush current is likely tooccur only at the time of activation. Therefore, to avoid loss caused bythe thermistor, a current is made to flow through the above thyristorduring stable operation.

Further, there has been proposed a power supply device includingmultiple buck converters connected in parallel together between outputends of a DC power supply circuit (e.g., see document 2 [JP 2011-78218A]). For example, a load such as a light emitting diode array isconnected between output ends of each buck converter. The aforementionedDC power supply circuit may be, for example, a capacitor for smoothing apulsating output of a diode bridge, a conventional boost converter, orthe like. In this power supply device, the multiple buck converters canshare the DC power supply circuit, but can be different from each otherin specifications and operations.

The power supply device including the DC power supply circuit and themultiple buck converters as with document 2 can be modified so that theparallel circuit of the thermistor and the thyristor is interposed inthe power supply path to the DC power supply circuit as with document 1.

With regard to the power supply device as modified above, it is assumedthat the circuit of the power supply device is designed so that thethyristor is kept on while any of the buck converters operates stably.In this case, even if in one or some of buck converters a switchingelement may be short-circuited and excess current may flow, thethermistor cannot provide effects of suppression of current while theother(s) of buck converters operates stably.

SUMMARY OF INVENTION

In view of the above insufficiency, the present invention has aimed topropose a power supply device with improved safety.

The power supply device of the first aspect in accordance with thepresent invention, includes: a parallel circuit of a thyristor and athermistor having a positive temperature coefficient; a DC power supplycircuit having a pair of output ends and being to receive power throughthe parallel circuit; and multiple buck converters connected in parallelwith each other between the pair of output ends of the DC power supplycircuit. The multiple buck converters include a main converter and atleast one sub converter. Each of the main converter and the at least onesub converter includes: a series circuit which is composed of a diodeand a switching element and is connected between the pair of output endsof the DC power supply circuit; a series circuit which is composed of acapacitor and an inductor and is connected in parallel with the diode;and a drive circuit configured to drive the switching element. The mainconverter further includes a secondary winding magnetically coupled withthe inductor of the main converter. The main converter is configured tocontrol the thyristor in accordance with a voltage across the secondarywinding of the main converter. The drive circuit of the main converteris configured to, when a short circuit of the switching element of theat least one sub converter occurs, terminate driving of the switchingelement of the main converter.

In the power supply device of the second aspect in accordance with thepresent invention which is realized in combination with the firstaspect, the at least one sub converter includes a secondary windingmagnetically coupled with the inductor of the at least one subconverter. The drive circuit of the main converter is configured to,when a voltage across the secondary winding of the at least one subconverter falls below a reference voltage, determine that a shortcircuit of the switching element of the at least one sub converteroccurs.

In the power supply device of the third aspect in accordance with thepresent invention which is realized in combination with the first orsecond aspect, the drive circuit of the main converter is configured todrive the switching element of the main converter in spite of whether ashort circuit of the switching element of the at least one sub converteroccurs, until predetermined delay time elapses after activation.

In the power supply device of the fourth aspect in accordance with thepresent invention which is realized in combination with any one of thefirst to third aspects, the main converter is configured to, when avoltage across the secondary winding of the main converter exceeds aprescribed voltage, turn on the thyristor.

In the power supply device of the fifth aspect in accordance with thepresent invention which is realized in combination with any one of thefirst to fourth aspects, the DC power supply circuit is configured touse supplied power to generate a predetermined DC voltage between thepair of output ends.

In the power supply device of the sixth aspect in accordance with thepresent invention which is realized in combination with any one of thefirst to fifth aspects, the drive circuit of each of the multiple buckconverters is configured to drive the switching element to adjust avoltage between opposite ends of the capacitor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit block diagram illustrating a power supply device ofone embodiment in accordance with the present invention.

FIG. 2 is a circuit block diagram illustrating a comparative example ofthe power supply device.

FIG. 3 is an explanatory diagram illustrating operations of the powersupply device.

FIG. 4 is an explanatory diagram illustrating operations of the powersupply device.

FIG. 5 is a circuit block diagram illustrating a modification of thepower supply device.

DESCRIPTION OF EMBODIMENTS

As shown in FIG. 1, a power supply device of an embodiment in accordancewith the present invention includes: a parallel circuit 4 of a thyristorQ0 and a thermistor PTH having a positive temperature property (positivetemperature coefficient); a boost converter 1 serving as a DC powersupply circuit to receive power through this parallel circuit 4; andmultiple buck converters 20 (21, 22) connected in parallel with eachother between output ends 11 and 12 of the boost converter 1.

Further, the power supply device of the present embodiment includes adiode bridge 31 which performs full-wave rectification on an AC currentinputted from an AC power supply AC to input a resultant current intothe boost converter 1 via the above parallel circuit. Additionally, thepower supply device of the present embodiment includes a filter circuit30 provided between the AC power supply AC and the diode bridge 31. Forexample, the filter circuit 30 may include a common mode choke coil toreduce noises. An output end of the diode bridge 31 for receiving alower potential and the output end 12 of the boost converter 1 forreceiving a lower potential are grounded.

The DC power supply circuit (boost converter) 1 is configured to usesupplied power to generate a predetermined DC voltage between the pairof output ends 11 and 12. The boost converter 1 is a conventionalcircuit which is also referred to as a step-up converter, a step-upchopper circuit, and a power factor correction circuit, and provides aneffect of improving input current distortion. Note that, the DC powersupply circuit may not be limited to the above boost converter 1, butmay include a capacitor for smoothing a DC output (pulsating currentoutput) of the diode bridge 31.

As described above, the parallel circuit 4 includes the thyristor Q0,and the thermistor PTH having a positive temperature property (positivetemperature coefficient). The thyristor Q0 has an anode connected to anoutput end of the diode bridge 31 for receiving a higher potential, anda cathode connected to an output end of the DC power supply circuit 1for receiving a higher potential. The thermistor PTH is connected inparallel with the thyristor Q0. Therefore, while the thyristor Q0 isoff, a current flows through the thermistor PTH. In contrast, while thethyristor Q0 is on, a current flows through not the thermistor PTH butthe thyristor Q0. In brief, while the thyristor Q0 is off, the parallelcircuit 4 suppresses an excess current such as an inrush current. Thethermistor PTH has such a temperature property that resistancesignificantly varies with temperature. For example, a resistance of thethermistor PTH at 160° C. is approximate 100 times as high as aresistance of the thermistor PTH at 25° C.

The multiple buck converters 21 and 22 include diodes D1 and D2 havingcathodes connected to the output end of the boost converter 1 forreceiving a higher potential, switching elements Q1 and Q2 having oneends connected to anodes of the diodes D1 and D2 and other endsconnected to the output end of the boost converter 1 for receiving alower potential, via resistors R1 and R2, and drive circuits 210 and 220configured to turn on and off the switching elements Q1 and Q2,respectively.

The above switching elements Q1 and Q2 may be MOSFETs, for example.

Further, in the buck converter 21, 22, a series circuit of a capacitor(output capacitor) C1, C2 and a primary winding N11, N21 of atransformer T1, T2 is connected between both ends of the diode D1, D2.The capacitor C1, C2 has both ends serving as the output ends of thebuck converter 21, 22. The capacitor C1, C2 is, for example, anelectrolytic capacitor.

In other words, the primary winding (inductor) N11, N21 of thetransformer T1, T2 constitutes a loop together with the diode D1, D2 andthe output capacitor C1, C2, and acts as an inductor to repeat storingand discharging power in accordance with on and off states of theswitching element Q1, Q2.

A light emitting diode LD1, LD2 is connected between the output ends(i.e., the both ends of the output capacitor C1, C2) of the buckconverter 21, 22.

The drive circuit 210, 220 changes a duty cycle or a switching frequencyof the switching element Q1, Q2 at appropriate timings so that an outputcurrent I1, I2 supplied to the light emitting diode LD1, LD2 is keptconstant. These drive circuits 210 and 220 can be realized based onconventional techniques, and detailed drawings and explanations of themare omitted.

One of the buck converters 21 and 22 is a main converter 21 configuredto turn on the thyristor Q0 in accordance with a voltage induced in thesecondary winding N12 of the transformer T1.

The drive circuit 210 of the main converter 21 terminates driving of theswitching element Q1 when a short circuit of the switching element Q2 ofthe other buck converter (hereinafter referred to as “sub converter”) 22occurs. In this regard, the short circuit of the switching element Q2means a short circuit causing the switching element Q2 to be kept on,such as a short circuit between a drain and a source.

In brief, the multiple buck converters 20 include the main converter 21and the sub converter (22, 23).

The main converter 21 includes a series circuit of the diode (firstdiode) D1 and the switching element (first switching element) Q1, aseries circuit of the capacitor (first capacitor) C1 and the inductor(first inductor) N11, and the drive circuit (first drive circuit) 210configured to drive the switching element (first switching element) Q1.The series circuit of the first diode D1 and the first switching elementQ1 is connected between the pair of output ends 11 and 12 of the DCpower supply circuit 1. In FIG. 1, the series circuit of the first diodeD1 and the first switching element Q1 is connected between the pair ofoutput ends 11 and 12 through the resistor R1. The resistor R1 isconnected between the first switching element Q1 and the output end 12.For example, the resistor R1 is a resistor for measuring a currentflowing through the first switching element Q1, and is used for decidinga timing of turning off the first switching element Q1. The seriescircuit of the first capacitor C1 and the first inductor N11 isconnected in parallel with the first diode D1. The first drive circuit210 is configured to drive (perform switching control on, or on/offcontrol on) the first switching element Q1 to adjust a voltage betweenopposite ends of the first capacitor C1. The main converter 21 furtherincludes the secondary winding (first secondary winding) N12magnetically coupled with the first inductor N11.

The sub converter 22 includes a series circuit of the diode (seconddiode) D2 and the switching element (second switching element) Q2, aseries circuit of the capacitor (second capacitor) C2 and the inductor(second inductor) N21, and the drive circuit (second drive circuit) 220configured to drive the switching element (second switching element) Q2.The series circuit of the second diode D2 and the second switchingelement Q2 is connected between the pair of output ends 11 and 12 of theDC power supply circuit 1. In FIG. 1, the series circuit of the seconddiode D2 and the second switching element Q2 is connected between thepair of output ends 11 and 12 via the resistor R2. The resistor R2 isconnected between the second switching element Q2 and the output end 12.For example, the resistor R2 is a resistor for measuring a currentflowing through the second switching element Q2, and is used fordeciding a timing of turning off the second switching element Q2. Theseries circuit of the second capacitor C2 and the second inductor N21 isconnected in parallel with the second diode D2. The second drive circuit220 is configured to drive (perform switching control on, or on/offcontrol on) the second switching element Q2 to adjust a voltage betweenopposite ends of the second capacitor C2.

As shown in FIG. 1, a voltage across the secondary winding N12 isinputted into a control circuit 5 for controlling the thyristor Q0. Thecontrol circuit 5 includes a capacitor C11, resistors R11 and R12, and adiode D11. The secondary winding N12 has one end connected to an inputterminal of the DC power supply circuit 1 for receiving a higherpotential, and another end connected to an anode of the diode D11. Thediode D11 has a cathode connected to the input terminal of the DC powersupply circuit 1 for receiving a higher potential, through a seriescircuit of the resistors R11 and R12 (i.e., a voltage dividing circuit).A connection point of the resistors R11 and R12 is connected to a gateof the thyristor Q0. The capacitor C11 is connected in parallel with theresistor R12.

Accordingly, a voltage induced in the secondary winding N12 of thetransformer T1 of the main converter 21 is half-wave rectified by thediode D11, and divided by the resistors R11 and R12, and smoothed by thecapacitor C11, and then impressed between the gate and the cathode ofthe thyristor Q0.

Therefore, the main converter 21 controls the thyristor Q0 in accordancewith the voltage across the first secondary winding N12. Especially,when the voltage across the first secondary winding N12 exceeds aprescribed voltage, the main converter 21 turns on the thyristor Q0. Theprescribed voltage is decided such that the thyristor Q0 is kept onwhile a current flows through the first inductor N11.

As shown in FIG. 1, a voltage across the secondary winding N22 isimpressed on the drive circuit 210 by a voltage detection circuit 6. Thevoltage detection circuit 6 includes a capacitor C21, resistors R21 andR22, and a diode D21. The secondary winding N22 has one end connected tothe output terminal 12 of the DC power supply circuit 1 for receiving alower potential, and another end connected to an anode of the diode D21.The diode D21 has a cathode connected to the output terminal 12 of theDC power supply circuit 1 for receiving a lower potential, through aseries circuit of the resistors R21 and R22 (i.e., a voltage dividingcircuit). A connection point of the resistors R21 and R22 is connectedto the drive circuit 210. The capacitor C21 is connected in parallelwith the resistor R22.

Accordingly, a voltage induced in the secondary winding N22 of thetransformer T2 of the sub converter 22 is half-wave rectified by thediode D21, and divided by the resistors R21 and R22, and smoothed by thecapacitor C21, and then inputted in the drive circuit 210 of the mainconverter 21 as a detection voltage Vd.

The drive circuit 210 of the main converter 21 compares the abovedetection voltage Vd inputted from the sub converter 22 with apredetermined reference voltage Vr. When the detection voltage Vd fallsbelow the reference voltage Vr, the drive circuit 210 of the mainconverter 21 determines that the switching element Q2 in another buckconverter (sub converter) 22 is short-circuited, and then terminatesdriving of the switching element Q1. In summary, when a short circuit ofthe second switching element Q2 of the sub converter 22 occurs, thefirst drive circuit 210 terminates driving of the first switchingelement Q1.

When driving of the switching element Q1 in the main converter 21 isterminated by the above operation, or when a short circuit of theswitching element Q1 of the main converter 21 occurs, a voltage is notinduced in the secondary winding N12 of the transformer T1 of the mainconverter 21. As a result, a voltage is no longer inputted into the gateof the thyristor Q0 and thus the thyristor Q0 is turned off. Thereafterthe thermistor PTH suppresses a current.

FIG. 2 shows a comparative example of the power supply device of thepresent embodiment. As shown in FIG. 2, in the comparative example, allof the buck converters 20 (21 and 22) are connected to the thyristor Q0,and the on control on the thyristor Q0 is performed in accordance withany of voltages across the secondary windings (N12 and N22) of thetransformers (T1 and T2) of the buck converters 20 (21 and 22).

In the case of the comparative example, the thyristor Q0 is turned offonly when all of short circuits of the switching elements Q1 and Q2 ofthe buck converter 21 and 22 occur. Therefore, even in a case where anyof short circuits of the switching elements Q1 and Q2 of the buckconverter 21 and 22 occurs, if at least one of the buck converters 21and 22 still operates, the thyristor Q0 is not turned off, andsuppression of current by the thermistor PTH is not realized.

Hence, abnormal heating possibly occurs in the buck converters 21 and 22in which the switching elements Q1 and Q2 are short-circuited and loadssuch as the light emitting diodes LD1 and LD2 connected to them.

In contrast, in the power supply device of the present embodiment, evenwhen any of short circuits of the switching elements (Q1, Q2) of thebuck converters 20 (21, 22) occurs, the thyristor Q0 is turned off andsuppression of current by the thermistor PTH becomes effective.Therefore, in contrast to the comparative example shown in FIG. 2, thepresent embodiment can provide improved safety.

Further, the thermistor PTH for suppressing rush currents is also usedfor suppressing currents resulting from a short circuit of the switchingelement (Q1, Q2) of the buck converter 20 (21, 22). Therefore, incontrast to a case of providing an additional protective element such asfuse, the power supply device of the present embodiment can be producedat a lowered cost.

FIG. 3 shows examples of time variations of on and off states of theswitching element Q2 of the sub converter 22, a voltage (hereinafterreferred to as “induced and rectified voltage”) Vi obtained by half-waverectification on the voltage across the secondary winding N22 of thetransformer T2 of the sub converter 22, the output current I2 of the subconverter 22, the detection voltage Vd, on and off states of theswitching element Q1 of the main converter 21, and the output current I1of the main converter 21. In FIG. 3, the horizontal axis indicateselapsed time from activation and this definition is also used in FIG. 4described later.

As shown in FIG. 3, the detection voltage Vd in the sub converter 22 iszero immediately after activation, and gradually increases with timefrom activation. Therefore, when the drive circuit 210 of the mainconverter 21 operates depending on the detection voltage Vd of the subconverter 22 from the time of activation, driving of the switchingelement Q1 in the main converter 21 does not start until the detectionvoltage Vd in the sub converter 22 reaches the reference voltage Vr.

As a result, a timing at which the light emitting diode LD1 connected tothe main converter 21 is turned on is likely to delay from a timing atwhich the light emitting diode LD2 connected to the sub converter 22 isturned on.

In view of this, as shown in FIG. 4, the drive circuit 210 of the mainconverter 21 may drive the switching element Q1 regardless of thedetection voltage Vd of the sub converter 22 (i.e., regardless ofwhether a short circuit of the switching element Q2 of the sub converter22 occurs) during a period (starting period) which starts afteractivation and ends after a lapse of predetermined delay time t1 fromthe activation. Note that, the phrase “after activation” means that“after supply of power from the AC power supply AC to the power supplydevice starts” or “after the drive circuit 210 starts to operate”, forexample.

To realize the aforementioned operation, the drive circuit 210 mayignore a result of comparison of the detection voltage Vd with thereference voltage Vr during the starting period. Alternatively, torealize the aforementioned operation, the reference voltage Vr may bekept equal to 0 (which means a voltage surely lower than the detectionvoltage Vd) during the starting period.

It is desirable that the aforementioned delay time t1 is surely longerthan time t0 necessary for the detection voltage Vd to reach thereference voltage Vr after activation but is short as possible.

The above configuration can prevent an unwanted situation in which thelight emitting diode LD1 connected to the main converter 21 is turned onafter the light emitting diode LD2 connected to the sub converter 22 isturned on, as shown in the examples of FIG. 3.

Note that, in FIG. 1, the only one sub converter 22 is provided.However, in FIG. 5, two or more sub converters 22, 23 may be provided.In short, the multiple buck converters 20 may include the main converter21 and at least one sub converter (22, 23).

The sub converter 23 includes a series circuit of a diode (second diode)D3 and a switching element (second switching element) Q3, a seriescircuit of a capacitor (second capacitor) C3 and an inductor (secondinductor) N31, and a drive circuit (second drive circuit) 230 configuredto drive the switching element (second switching element) Q3. The seriescircuit of the second diode D3 and the second switching element Q3 isconnected between the pair of output ends 11 and 12 of the DC powersupply circuit 1. In FIG. 5, the series circuit of the second diode D3and the second switching element Q3 is connected between the pair ofoutput ends 11 and 12 via a resistor R3. The resistor R3 is connectedbetween the second switching element Q3 and the output end 12. Forexample, the resistor R3 is a resistor for measuring a current flowingthrough the second switching element Q3, and is used for deciding atiming of turning off the second switching element Q3. The seriescircuit of the second capacitor C3 and the second inductor N31 isconnected in parallel with the second diode D3. The second drive circuit230 is configured to drive (perform switching control on, or on/offcontrol on) the second switching element Q3 to adjust a voltage betweenopposite ends of the second capacitor C3.

As described above, the sub converter (second sub converter) 23 shown ina lower part of FIG. 5 is different in reference signs from the othersub converter (first sub converter) 22, but is the same in circuitconfigurations and operations as the first sub converter 22, andtherefore detailed explanations are omitted.

In the example shown in FIG. 5, a voltage across the secondary windingN22 is given to a comparison circuit 7 by the voltage detection circuit6. Further, a voltage across a secondary winding N32 is given to thecomparison circuit 7 by a voltage detection circuit 61.

The voltage detection circuit 61 includes a capacitor C31, resistors R31and R32, and a diode D31. The secondary winding N32 has one endconnected to the output terminal 12 of the DC power supply circuit 1 forreceiving a lower potential, and another end connected to an anode ofthe diode D31. The diode D31 has a cathode connected to the outputterminal 12 of the DC power supply circuit 1 for a lower potential,through a series circuit of the resistors R31 and R32 (i.e., a voltagedividing circuit). A connection point of the resistors R31 and R32 isconnected to the comparison circuit 7. The capacitor C31 is connected inparallel with the resistor R32.

The comparison circuit 7 includes comparators CP and CP1, and an ANDcircuit AND. The comparator CP has a non-inverting input terminalconnected to the connection point of the resistors R21 and R22 of thevoltage detection circuit 6, and an inverting input terminal connectedto a voltage source E1 providing the reference voltage Vr. Thecomparator CP1 has a non-inverting input terminal connected to theconnection point of the resistors R31 and R32 of the voltage detectioncircuit 61, and an inverting input terminal connected to a voltagesource E2 providing a reference voltage Vr1. The AND circuit AND has oneinput terminal connected to an output terminal of the comparator CP,another input terminal connected to an output terminal of the comparatorCP1, and an output terminal connected to the drive circuit 210.

In short, in the example of FIG. 5, comparators (hereinafter referred toas “detection comparators”) CP and CP1 for comparing the detectionvoltages Vd and Vd1 with the reference voltages Vr and Vr1 are providedindividually to the sub converters 22 and 23. The AND circuit ANDreceives outputs from all of the detection comparators CP and CP1 andthen provides an output to the drive circuit 210 of the main converter21.

In the example of FIG. 5, when the output of the aforementioned ANDcircuit AND turns into an L level, the drive circuit 210 of the mainconverter 21 determines that any of short circuits of the switchingelements Q2 and Q3 of the sub converters 22 and 23 occurs, and thenterminates driving of the switching element Q1.

In other words, only while all of the detection voltages Vd and Vd1 ofthe sub converters 22 and 23 occur normally, the switching element Q1 inthe main converter 21 is kept being driven and then the thyristor Q0 iskept on.

Further, in the example of FIG. 5, the drive circuit 210 of the mainconverter 21 may drive the switching element Q1 regardless of the outputfrom the AND circuit AND during the aforementioned starting period.

As described above, the power supply device of the present embodimentincludes the following first to sixth features.

In the first feature, the power supply device includes: the parallelcircuit 4 of the thyristor Q0 and the thermistor PTH having a positivetemperature property; the DC power supply circuit 1 to receive powerthrough the parallel circuit 4; and multiple buck converters 20connected in parallel with each other between output ends of the DCpower supply circuit 1. Each of the buck converters 20 (21, 22, 23)includes: a series circuit which is defined as a series circuit of thediode (D1, D2, D3) and the switching element (Q1, Q2, Q3) and isconnected between output ends of the DC power supply circuit 1; thecapacitor (C1, C2, C3) having opposite ends serving as the output ends;the inductor (N11, N21, N31) constituting a loop together with the diode(D1, D2, D3) and the capacitor (C1, C2, C3); and the drive circuit (210,220, 230) configured to drive the switching element (Q1, Q2, Q3). One ofthe multiple buck converters 20 serves as the main converter 21 whichincludes the secondary winding N12 associated with the inductor N11 andis to turn on the thyristor Q0 in accordance with a voltage induced inthe secondary winding N12. When a short circuit of the switching element(Q2, Q3) of any of the other buck converters 20 (22, 23) occurs, thedrive circuit 210 of the main converter 21 terminates driving of theswitching element Q1.

In other words, the power supply device includes: a parallel circuit 4of a thyristor Q0 and a thermistor PTH having a positive temperaturecoefficient; a DC power supply circuit (the boost converter) 1 having apair of output ends 11 and 12 and being to receive power through theparallel circuit 4; and multiple buck converters 20 connected inparallel with each other between the pair of output ends 11 and 12 ofthe DC power supply circuit 1. The multiple buck converters 20 include amain converter 21 and at least one sub converter (22, 23). Each of themain converter 21 and the at least one sub converter (22, 23) includes:a series circuit composed of a diode (D1, D2, D3) and a switchingelement (Q1, Q2, Q3); a series circuit composed of a capacitor (C1, C2,C3) and an inductor (N11, N21, N31); and a drive circuit (210, 220, 230)configured to drive the switching element (Q1, Q2, Q3). The seriescircuit composed of the diode (D1, D2, D3) and the switching element(Q1, Q2, Q3) is connected between the pair of output ends 11 and 12 ofthe DC power supply circuit 1. The series circuit composed of thecapacitor (C1, C2, C3) and the inductor (N11, N21, N31) is connected inparallel with the diode (D1, D2, D3). The main converter 21 furtherincludes a (first) secondary winding N12 magnetically coupled with the(first) inductor N11 of the main converter 21. The main converter 21 isconfigured to control the thyristor Q0 in accordance with a voltageacross the (first) secondary winding N12 of the main converter 21. The(first) drive circuit 210 of the main converter 21 is configured to,when a short circuit of the (second) switching element (Q2, Q3) of theat least one sub converter (22, 23) occurs, terminate driving of the(first) switching element Q1 of the main converter 21.

In the second feature realized in combination with the first feature,with regard to all of the buck converters 20 (22, 23) other than themain converter 21, the inductor (N21, N31) is associated with thesecondary winding (N22, N32). When a voltage does not occur across thesecondary winding (N22, N32) of any of the other buck converters 20 (22,23), the drive circuit 210 of the main converter 21 terminates drivingof the switching element Q1. In other words, the at least one subconverter (22, 23) includes a (second) secondary winding (N21, N22)magnetically coupled with the (second) inductor (N21, N31) of the atleast one sub converter (22, 23). The (first) drive circuit 210 of themain converter 21 is configured to, when a voltage across the (second)secondary winding (N22, N32) of the at least one sub converter (22, 23)falls below a reference voltage, determine that a short circuit of the(second) switching element (Q2, Q3) of the at least one sub converter(22, 23) occurs. Note that, the second feature is optional.

In the third feature realized in combination with the first or secondfeature, the drive circuit 210 of the main converter 21 drives theswitching element Q1 regardless of whether a short circuit of theswitching element (Q2, Q3) of another buck converter 20 (22, 23) untilpredetermined delay time t1 elapses after activation. In other words,the (first) drive circuit 210 of the main converter 21 is configured todrive the (first) switching element Q1 of the main converter 21 in spiteof whether a short circuit of the (second) switching element (Q2, Q3) ofthe at least one sub converter (22, 23) occurs, until predetermineddelay time t1 elapses after activation. Note that, the third feature isoptional.

In the fourth feature realized in combination with any one of the firstto third features, the main converter 21 is configured to, when avoltage across the (first) secondary winding N12 of the main converter21 exceeds a prescribed voltage, turn on the thyristor Q0. Note that,the fourth feature is optional.

In the fifth feature realized in combination with any one of the firstto fourth features, the DC power supply circuit (the boost converter) 1is configured to use supplied power to generate a predetermined DCvoltage between the pair of output ends 11 and 12. Note that, the fifthfeature is optional.

In the sixth feature realized in combination with any one of the firstto fifth features, the drive circuit (210, 220, 230) of each of themultiple buck converters 20 is configured to drive the switching element(Q1, Q2, Q3) to adjust a voltage between opposite ends of the capacitor(C1, C2, C3). Note that, the sixth feature is optional.

According to the aforementioned power supply device of the presentembodiment, even when any of short circuits of the switching elements(Q2, Q3) of the buck converters 20 occurs, the thyristor Q0 is turnedoff and suppression of current by the thermistor PTH becomes effective.Therefore, in contrast to a case where the thyristor Q0 is turned offonly when all of short circuits of the switching elements (Q1, Q2, Q3)of the buck converters 20 occur, the present embodiment can provideimproved safety.

1. A power supply device comprising: a parallel circuit of a thyristorand a thermistor having a positive temperature coefficient; a DC powersupply circuit having a pair of output ends and being to receive powerthrough the parallel circuit; and multiple buck converters connected inparallel with each other between the pair of output ends of the DC powersupply circuit, the multiple buck converters including a main converterand at least one sub converter, each of the main converter and the atleast one sub converter including a series circuit which is composed ofa diode and a switching element and is connected between the pair ofoutput ends of the DC power supply circuit, a series circuit which iscomposed of a capacitor and an inductor and is connected in parallelwith the diode, and a drive circuit configured to drive the switchingelement, the main converter further including a secondary windingmagnetically coupled with the inductor of the main converter, the mainconverter being configured to control the thyristor in accordance with avoltage across the secondary winding of the main converter, and thedrive circuit of the main converter being configured to, when a shortcircuit of the switching element of the at least one sub converteroccurs, terminate driving of the switching element of the mainconverter.
 2. The power supply device according to claim 1, wherein: theat least one sub converter includes a secondary winding magneticallycoupled with the inductor of the at least one sub converter; and thedrive circuit of the main converter is configured to, when a voltageacross the secondary winding of the at least one sub converter fallsbelow a reference voltage, determine that a short circuit of theswitching element of the at least one sub converter occurs.
 3. The powersupply device according to claim 1, wherein the drive circuit of themain converter is configured to drive the switching element of the mainconverter in spite of whether a short circuit of the switching elementof the at least one sub converter occurs, until predetermined delay timeelapses after activation.
 4. The power supply device according to claim1, wherein the main converter is configured to, when a voltage acrossthe secondary winding of the main converter exceeds a prescribedvoltage, turn on the thyristor.
 5. The power supply device according toclaim 1, wherein the DC power supply circuit is configured to usesupplied power to generate a predetermined DC voltage between the pairof output ends.
 6. The power supply device according to claim 1, whereinthe drive circuit of each of the multiple buck converters is configuredto drive the switching element to adjust a voltage between opposite endsof the capacitor.